Synthesis, crystal structure, and magnetic properties of a very rare double μ-1,1-azido- and a μ-1,1-(OMe)-bridged FeIII dimer containing a N,N,O-donor tridentate Schiff base ligand

Two new Fe-III complexes, [Fe2L2(mu-OMe)(2)(NCS)(2)] (1) and [Fe2L2(mu-N-3)(2)(N-3)(2)] (2), have been synthesized using a N,N,O-donor tridentate Schiff base ligand HL {2-[(2-dimethylaminoethylimino)methyl]phenol}, the condensation product of salicylaldehyde and N,N-dimethyl-1,2-diaminoethane. The complexes were characterized by X-ray structural analyses and variable-temperature magnetic susceptibility measurements. Both crystal structures are centrosymmetric dimers containing two Fe-III atoms, which are bridged in compound 1 by two methoxy anions and in compound 2 by two mu-1,1-azides. The chelating tridentate Schiff base and a terminal thiocyanato (for 1) or azido (for 2) group complete the hexacoordination of the distorted octahedral environment of each iron center. The magnetic properties of compound 1 show the presence of antiferromagnetic exchange interactions mediated by double methoxy bridges (J = -29.45 cm(-1)). Compound 2 shows the presence of very weak ferromagnetic exchange interactions mediated by double mu-1,1-N-3 bridges (J = 1.08 cm(-1)).

Synthesis and characterization of nickel(II) and copper(II) complexes with tetradentate Schiff base ligands

The 1:1 condensation of 1,2-diaminopropane and 1-phenylbutane-1,3-dione at high dilution gives a mixture of two positional isomers of terdentate mono-condensed Schiff bases 6-amino-3-methyl-1-phenyl-4-aza-2-hepten-1-one (HAMPAH) and 6-amino-3,5-dimethyl-1-phenyl-4-aza-2-hexen-1-one (HADPAH). The mixture of the terdentate ligands has been used for further condensation with pyridine-2-carboxaldehyde or 2-acetylpyridine to obtain the unsymmetrical tetradentate Schiff base ligands. The tetradentate Schiff bases are then allowed to react with the methanol solution of copper(II) and nickel(II) perchlorate separately. The X-ray diffraction confirms the structures of two of the complexes and shows that the condensation site of the diamine with 1-phenylbutane-1,3-dione is the same.

Syntheses, characterization and X-ray crystal structures of a mono- and a penta-nuclear nickel(II) complex with oximato Schiff base ligands

A mononuclear octahedral nickel(II) complex [Ni(HL(1))(2)](SCN)(2) (1) and an unusual penta-nuclear complex [{(NiL(2))(mu-SCN)}(4)Ni(NCS)(2)]center dot 2CH(3)CN (2) where HL(1) = 3-(2-aminoethylimino)butan-2-one oxime and HL(2) = 3-(hydroxyimino)butan-2-ylidene)amino)propylimino)butan-2-one oxime have been prepared and characterized by X-ray crystallography. The mono-condensed ligand, HL(1), was prepared by the 1:1 condensation of the 1,2-diaminoethane with diacetylmonoxime in methanol under high dilution. Complex 1 is found to be a mer isomer and the amine hydrogen atoms are involved in extensive hydrogen bonding with the thiocyanate anions. The dicondensed ligand, HL(2), was prepared by the 1:2 condensation of the 1,3-diaminopropane with diacetylmonoxime in methanol. The central nickel(II) in 2 is coordinated by six nitrogen atoms of six thiocyanate groups, four of which utilize their sulphur atoms to connect four NiL2 moieties to form a penta-nuclear complex and it is unique in the sense that this is the first thiocyanato bridged penta-nuclear nickel(II) compound with Schiff base ligands.

Structural and magnetic studies of Schiff base complexes of nickel(ii) nitrite: change in crystalline state, ligand rearrangement and a very rare μ-nitrito-1κO:2κN:3κO′ bridging mode

Four new nickel(II) complexes, [Ni2L2(NO2)2]·CH2Cl2·C2H5OH, 2H2O (1), [Ni2L2(DMF)2(m-NO2)]ClO4·DMF (2a), [Ni2L2(DMF)2(m-NO2)]ClO4 (2b) and [Ni3L¢2(m3-NO2)2(CH2Cl2)]n·1.5H2O (3) where HL = 2-[(3-amino-propylimino)-methyl]-phenol, H2L¢ = 2-({3-[(2-hydroxy-benzylidene)-amino]-propylimino}-methyl)-phenol and DMF = N,N-dimethylformamide, have been synthesized starting with the precursor complex [NiL2]·2H2O, nickel(II) perchlorate and sodium nitrite and characterized structurally and magnetically. The structural analyses reveal that in all the complexes, NiII ions possess a distorted octahedral geometry. Complex 1 is a dinuclear di-m2-phenoxo bridged species in which nitrite ion acts as chelating co-ligand. Complexes 2a and 2b also consist of dinuclear entities, but in these two compounds a cis-(m-nitrito-1kO:2kN) bridge is present in addition to the di-m2-phenoxo bridge. The molecular structures of 2a and 2b are equivalent; they differ only in that 2a contains an additional solvated DMF molecule. Complex 3 is formed by ligand rearrangement and is a one-dimensional polymer in which double phenoxo as well as m-nitrito-1kO:2kN bridged trinuclear units are linked through a very rare m3-nitrito-1kO:2kN:3kO¢ bridge. Analysis of variable-temperature magnetic susceptibility data indicates that there is a global weak antiferromagnetic interaction between the nickel(II) ions in four complexes, with exchange parameters J of -5.26, -11.45, -10.66 and -5.99 cm-1 for 1, 2a, 2b and 3, respectively

Anion-directed template synthesis and hydrolysis of mono-condensed Schiff base of 1,3-pentanediamine ando-hydroxyacetophenone in NiII and CuII Complexes

Bis(o-hydroxyacetophenone)nickel(II) dihydrate, on reaction with 1,3-pentanediamine, yields a bis-chelate complex [NiL2]·2H2O (1) of mono-condensed tridentate Schiff baseligand HL {2-[1-(3-aminopentylimino)ethyl]phenol}. The Schiff base has been freed from the complex by precipitating the NiII as a dimethylglyoximato complex. HL reacts smoothly with Ni(SCN)2·4H2O furnishing the complex [NiL(NCS)] (2) and with CuCl2·2H2O in the presence of NaN3 or NH4SCN producing [CuL(N3)]2 (3) or [CuL(NCS)] (4). On the other hand, upon reaction with Cu(ClO4)2·6H2O and Cu(NO3)2·3H2O, the Schiff base undergoes hydrolysis to yield ternary complexes [Cu(hap)(pn)(H2O)]ClO4 (5) and [Cu(hap)(pn)(H2O)]NO3 (6), respectively (Hhap = o-hydroxyacetophenone and pn = 1,3-pentanediamine). The ligand HL undergoes hydrolysis also on reaction with Ni(ClO4)2·6H2O or Ni(NO3)2·6H2O to yield [Ni(hap)2] (7). The structures of the complexes 2, 3, 5, 6, and 7 have been confirmed by single-crystal X-ray analysis. In complex 2, NiII possesses square-planar geometry, being coordinated by the tridentate mono-negative Schiff base, L and the isothiocyanate group. The coordination environment around CuII in complex 3 is very similar to that in complex 2 but here two units are joined together by end-on, axial-equatorial azide bridges to result in a dimer in which the geometry around CuII is square pyramidal. In both 5 and 6, the CuII atoms display the square-pyramidal environment; the equatorial sites being coordinated by the two amine groups of 1,3-pentanediamine and two oxygen atoms of o-hydroxyacetophenone. The axial site is coordinated by a water molecule. Complex 7 is a square-planar complex with the Ni atom bonded to four oxygen atoms from two hap moieties. The mononuclear units of 2 and dinuclear units of 3 are linked by strong hydrogen bonds to form a one-dimensional network. The mononuclear units of 5 and 6 are joined together to form a dimer by very strong hydrogen bonds through the coordinated water molecule. These dimers are further involved in hydrogen bonding with the respective counteranions to form 2-D net-like open frameworks.

The isatin-Schiff base copper(II) complex Cu(isaepy)(2) acts as delocalized lipophilic cation, yields widespread mitochondrial oxidative damage and induces AMP-activated protein kinase-dependent apoptosis

We previously demonstrated that Bis[(2-oxindol-3-ylimino)-2-(2-aminoethyl) pyridine-N, N`] copper(II) [Cu(isaepy)(2)] was an efficient inducer of the apoptotic mitochondrial pathway. Here, we deeply dissect the mechanisms underlying the ability of Cu(isaepy)(2) to cause mitochondriotoxicity. In particular, we demonstrate that Cu(isaepy)(2) increases NADH-dependent oxygen consumption of isolated mitochondria and that this phenomenon is associated with oxy-radical production and insensitive to adenosine diphosphate. These data indicate that Cu(isaepy)(2) behaves as an uncoupler and this property is also confirmed in cell systems. Particularly, SH-SY5Y cells show: (i) an early loss of mitochondrial transmembrane potential; (ii) a decrease in the expression levels of respiratory complex components and (iii) a significant adenosine triphosphate (ATP) decrement. The causative energetic impairment mediated by Cu(isaepy)(2) in apoptosis is confirmed by experiments carried out with rho(0) cells, or by glucose supplementation, where cell death is significantly inhibited. Moreover, gastric and cervix carcinoma AGS and HeLa cells, which rely most of their ATP production on oxidative phosphorylation, show a marked sensitivity toward Cu(isaepy)(2). Adenosine monophosphate-activated protein kinase (AMPK), which is activated by events increasing the adenosine monophosphate: ATP ratio, is deeply involved in the apoptotic process because the overexpression of its dominant/negative form completely abolishes cell death. Upon glucose supplementation, AMPK is not activated, confirming its role as fuel-sensing enzyme that positively responds to Cu(isaepy)(2)-mediated energetic impairment by committing cells to apoptosis. Overall, data obtained indicate that Cu(isaepy)(2) behaves as delocalized lipophilic cation and induces mitochondrial-sited reactive oxygen species production. This event results in mitochondrial dysfunction and ATP decrease, which in turn triggers AMPK-dependent apoptosis.

Double-strand DNA cleavage induced by oxindole-Schiff base copper(II) complexes with potential antitumor activity

Some oxindole-Schiff base copper(II) complexes have already shown potential antitumor activity towards different cells, inducing apoptosis in a process modulated by the ligand, and having nuclei and mitochondria as main targets. Here, three novel copper(II) complexes with analogous ligands were isolated and characterized by spectroscopic techniques, having their reactivity compared to the so far most active complex in this class. Cytotoxicity experiments carried out toward human neuroblastoma SH-SY5Y cells confirmed its proapoptosis property. DNA cleavage studies were then performed in the presence of these complexes, in order to verify the influence of ligand structural features in its nuclease activity. All of them were able to cause double-strand DNA scissions, giving rise to nicked circular Form II and linear Form III species, in the presence of hydrogen peroxide. Additionally, DNA Form II was also detected in the absence of peroxide when the most active complex, [Cu(isaepy)(2)](2+) 1, was used. In an effort to better elucidate their interactions with DNA, solutions of the different complexes titrated with DNA had their absorption spectra monitored. An absorbance hyperchromism observed at 260 nm pointed to the intercalation of these complexes into the DNA structure. Further, investigations of 2-deoxy-D-ribose (DR) oxidation catalyzed by each of those complexes, using 2-thiobarbituric acid reactive species (TBARS) method, and detection of reactive oxygen species (ROS) formation by spin-trapping EPR, suggested that their mechanism of action in performing efficiently DNA cleavage occurs preferentially, but not only by oxidative pathways. (C) 2007 Elsevier Inc. All rights reserved.

Oxindole-Schiff base copper(II) complexes interactions with human serum albumin: Spectroscopic, oxidative damage, and computational studies

CD and EPR were used to characterize interactions of oxindole-Schiff base copper(II) complexes with human serum albumin (HSA). These imine ligands form very stable complexes with copper, and can efficiently compete for this metal ion towards the specific N-terminal binding site of the protein, consisting of the amino acid sequence Asp-Ala-His. Relative stability constants for the corresponding complexes were estimated from CD data, using the protein as competitive ligand, with values of log K(CuL) in the range 15.7-18.1, very close to that of [Cu(HSA)] itself, with log K(CuHSA) 16.2. Some of the complexes are also able to interfere in the a-helix structure of the protein, while others seem not to affect it. EPR spectra corroborate those results, indicating at least two different metal species in solution, depending on the imine ligand. Oxidative damage to the protein after incubation with these copper(II) complexes, particularly in the presence of hydrogen peroxide, was monitored by carbonyl groups formation, and was observed to be more severe when conformational features of the protein were modified. Complementary EPR spin-trapping data indicated significant formation of hydroxyl and carbon centered radicals, consistent with an oxidative mechanism. Theoretical calculations at density functional theory (DFT) level were employed to evaluate Cu(II)-L binding energies, L -> Cu(II) donation, and Cu(II) -> L back-donation, by considering the Schiff bases and the N-terminal site of HSA as ligands. These results complement previous studies on cytotoxicity, nuclease and pro-apoptotic properties of this kind of copper(II) complexes, providing additional information about their possibilities of transport and disposition in blood plasma. (C) 2009 Elsevier Inc. All rights reserved.

Spectroscopic characterization of schiff base-copper complexes immobilized in smectite clays

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Synthesis, characterization and electropolymerization of a new polypyrrole iron(II) Schiff-base complex

This work presents the synthesis of the complex [Fe(L)(2)](PF6)(2) (.) H2O (L = 2,6-bis[1-(3-pyrrol-1-yl-propylimino)ethyl]pyridine (Fig. 1) and its characterization through elemental and thermal analysis, X-ray diffraction and UV-Vis, IR and H-1 NMR spectra. The use of this compound in the preparation of modified electrodes is also described. The best electrochemical parameters to achieve optimum film formation have been established and the effects of both the upper-limit of the applied scanning potential (E-aul) and the number of scans on the efficiency of film formation have been investigated. Film surface morphology has been characterized by atomic force microscopy. (C) 2004 Elsevier Ltd. All rights reserved.

Thermal decomposition of vanadyl Schiff-base compounds

The thermal stability and thermal decomposition of several Schiff bases coordinated to vanadyl, VO (Schiff base), were studied by thermogravimetry and conventional gas Chromatographic and X-ray analyses. The kinetics, the number of steps and, in particular, the final temperature of decomposition of these complexes depend on the equatorial ligand. © 1992.

Tetradentate schiff base copper(II) complexes

Ten copper(II) complexes of tetradentate Schiff bases obtained by condensing two moles of an o-hydroxyphenylcarbonyl compound with a diamine have been prepared and characterized by elemental analyses, melting points, IR and electronic spectra. The IR and electronic spectra of the free ligand and the complexes are compared and discussed. The deconvolution of the visible spectra of the complexes in CHCl3, approximately C2v or C1, yielded four peaks at ca. 15000, 17000, 18000-19000, and 20000-22000 cm-1, assigned to the four d-d transitions.

Coordinative versatility of a Schiff base containing thiophene: Synthesis, characterization and biological activity of zinc(II) and silver(I) complexes

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Electropolymerization using binuclear nickel(II) Schiff base complexes bearing N4O4 donors as supramolecular building blocks

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Isatin-Schiff base copper(II) complexes-A DFT study of the metal-ligand bonding situation

Herein, we report results of calculations based on density functional theory (BP86/TZVP) of a set of isatin-Schiff base copper(II) and related complexes, 1-12, that have shown significant pro-apoptotic activity toward diverse tumor cells. The interaction of the copper(II) cation with different ligands has been investigated at the same level of theory. The strength and character of the Cu(II)-L bonding was characterized by metal-ligand bond lengths, vibrational frequencies, binding energies, ligand deformation energies, and natural population analysis. The metal-ligand bonding situation was also characterized by using two complementary topological approaches, the quantum theory of atoms-in-molecules (QTAIM) and the electron localization function (ELF). The calculated electronic g-tensor and hyperfine coupling constants present significant agreement with the EPR experimental data. The calculated parameters pointed to complex 10 as the most stable among the isatin-Schiff base copper(II) species, in good agreement with experimental data that indicate this complex as the most reactive in the series. (C) 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012